The invention relates to the isolation of a biologically active hemagglutinin protein from the Clostridium botulinum type A neurotoxin complex.
Botulinum neurotoxins (BoNTs) are extremely potent proteins with a mouse lethal dose of 0.3 ng/kg. Seven serotypes (A-G) of BoNTs are produced by different strains of Clostridium botulinum. In addition, certain nonbotulinum species of Clostridium, such as C. butyricum and C. baratii, have been shown to produce the toxins. The neurotoxin is a protein of about 150 kDa and consists of two polypeptide chains (a 50 kDa light chain and a 100 kDa heavy chain), which are linked together via a disulfide bond.
BoNTs are often produced by bacteria under anaerobic conditions in improperly stored or processed foods. Ingestion of the contaminated food can cause the flaccid muscle paralysis known as botulism.
The mechanism by which BoNTs cause botulism has been well studied. After ingestion, the neurotoxin is translocated across the intestinal mucosa, gaining access to neuromuscular junctions. At affected junctions, the neurotoxin is internalized by neurons via endocytosis. Inside the cell, the toxin's protease activity degrades specific vesicular and plasma membrane proteins, disrupting neurotransmitter release from the neuron. Thus, the patient experiences paralysis due to an inability to release neurotransmitters from the presynaptic surface. This process is reviewed in Sakaguchi, Pharmac. Ther., 19:165-194 (1983).